Sprinkler system installers typically use metal conduit, either copper or more commonly iron or steel pipe, as supply lines in automatic sprinkler systems. Such metal lines obviously resist fire and temperature damage better than other structural materials that might be used.
Each metal has relative cost advantages and disadvantages. Typically, piping is provided in fixed lengths and must be cut to size prior to installation. Ferrous pipe was then typically threaded in the field and mated with a threaded coupling. The use of threaded couplings in ferrous piping adds significantly to the labor costs of installing such systems. Copper tubing installs more quickly than ferrous pipe as the cut lengths of copper can simply be slip-mated with appropriate fittings and then soldered. However, copper is quite expensive in material cost compared to ferrous pipe.
Other types of non-threaded mating systems have been developed for metal particularly steel pipe. For example, crimping systems are known in which crimpable fittings can be used to join small diameters of the lightest Schedule 5 steel piping. Other types of mechanical, compression type fittings are known which sealingly mate with the exterior ends of grooved piping. Still other types of mechanical joining systems employ a tubular insert positioned in each open end of a pair of adjoining piping members and an external compression fitting which is applied over the ends and the insert to compress the ends against the insert. Such systems require either the mechanical shaping and disruption of the smooth, cylindrical ends of the piping by the addition of grooves, flanges or the like and/or the use of unique and typically expensive compression fittings.
Certain plastics have gained acceptance for use in residential and, to some extent, light hazard fire sprinkler systems. Chlorinated polyvinyl chloride (CPVC) plastic piping and fittings have been listed by Underwriters Laboratories. One listed CPVC compound is BLAZEMASTER.RTM. brand CPVC of The B. F. Goodrich Co., Cleveland, Ohio. BLAZEMASTER.RTM. is a registered trademark of The B. F. Goodrich Co. Underwriters Laboratories has also listed Flameaway brand CPVC pipe and fittings distributed in the United States by Flameaway Plastics, Inc. of Beverly Hills, Calif. Underwriters Laboratories also lists certain polybutylene sprinkler pipe and fittings for use in residential and light hazard fire sprinkler systems.
Piping made from plastic has proved to be less expensive in material cost than copper while installation costs have been comparable to copper. Similar steps are involved in joining together both types of plastic and copper pipe. However, plastic piping is more flexible than metal piping. Support must be provided more frequently with plastic piping than with metal piping and more frequently with polybutylene than with CPVC. This can add sufficiently to both the material costs and the labor costs of installed plastic piping systems to actually raise the total costs of such plastic systems above the costs of metal systems in some installations. Plastic piping for sprinkler systems finds use primarily in residential installations where the plastic pipe can be more easily installed through misaligned openings and through and/or around rafters and joists than can metal piping.
According to recent industry figures, residential sprinkler heads account for about fifteen per cent of all sprinkler heads sold. However, because of the greater size of piping and more expensive sprinklers typically used in light and ordinary hazard installations, the actual dollar value of the residential sprinkler market is estimated to be only about ten per cent or less of the total dollar market for residential, light and ordinary hazard sprinkler installations.
Hybrid plastic/metal piping and couplings have been proposed for fluid conduit systems for many years.
For example, U.S. Pat. No. 5,143,407 to Cokeh refers to a proposal to use copper tubing coated with polyvinyl chloride (PVC) for protection against denting and discloses a variety of copper fittings partially coated with PVC for the formation of joints between the ends of lengths of such multilayer conduit. Cokeh does not indicate how such composite tubing is or could be made or if it has been made. The tubing is joined with the fittings by suitable plastic adhesive applied to the plastic outside surface of the conduit, which bonds to the PVC sleeve formed around the metal tube portion of the coupling. Compression fit is also described for securing the pipe ends to the coupling. However, in each instance, the use of resilient washers is disclosed to provide a leak-proof fluid seal. This is required because PVC does not bond to the copper.
Other types of plastic coated pipe have been proposed for other purposes. For example, U.S. Pat. No. 3,502,492 discloses the electrostatic deposition of a light dusting of an epoxy resin upon the surface of a metal substrate like the outer surface of a metal pipe, the electrostatic deposition of PVC resin particles upon the surface in a heavier layer and the heating of the substrate to coalesce the PVC and epoxy resins to form a PVC layer adhered to the surface of the substrate. Physical structure of the pipes or their joints are not discussed.
U.S. Pat. No. 4,481,239 discloses a process for coating metallic substrates such as iron pipe in which one or more crosslinking resins are applied to the pipe surface and heated sufficiently to crosslink and an olefin polymer is applied to the heated, coated substrate as an outer layer. Structures of the pipe or their joints are not discussed.
U.S. Pat. No. 2,646,822 discloses the use of polyethylene (PE) or polystyrene as a corrosion resistant external coating for metal pipes. In the only examples shown in that patent, the PE coated metal pipes were provided with plastic-free, conventionally threaded ends. The ends are shown being received in plastic-coated, metal couplings with plastic-free, internal metal threads to provide continuous lengths of plastic-coated metal pipe. Coupling at the joint is provided by mechanical engagement of threads on the outside end of the pipe with the threads inside the metal tubing of the coupling. There is no indication whether the plastic layer is adhered to the pipe.